JPH0652908B2 - Data transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In multi-drop data transmission using a pulse transformer, an open flag (OF) indicating the beginning of a frame.
By setting the frequency of the close flag (CF) indicating the end of the frame and the frequency of the data (“1” / “0”) to be lower than the frequency of the data (“1” / “0”), the OF signal is even By individually transmitting and transmitting an even number of pulse signals having a higher frequency than the CF signal after the CR signal, the influence on the transmission path after frame transmission is reduced.

[Industrial application field]

The present invention relates to multi-drop data transmission using a pulse transformer, and more particularly to a data transmission method for reducing distortion of a transmission waveform due to a transmission line and a load.

[Conventional technology]

As shown in FIG. 3, in the multi-drop method, terminating resistors 2 are connected to both ends of a transmission line 1 and n transmission devices 3 are connected between them.
Are connected. The transmission device 3 is insulated from the transmission line 1 by a pulse transformer 4. This system has a feature that an arbitrary number of transmission devices 3 can be connected to an arbitrary position of a transmission line. However, it also has the drawback of varying the load.

In the multi-drop method, there is a floating period (pause period) between frames. That is,
As shown in the frame structure in FIG. 4, the 5th frame is
6 open flags (OF) and 8 close flags (C
F) and seven data parts sandwiched by these OF and CF, and there is a floating period (pause period) between frames.

Next, as a modulation method in pulse transmission, the conventional PD
The M (alternating pulse modulation) method is known. An example of this modulation / demodulation is shown in FIG. 5, and this PD is shown in FIG. 5 (A).
The configuration of the M type transmission device is also shown in FIG.
In (G), an explanatory diagram of modulation / demodulation waveforms of the PDM system is shown. The transmission data of the transmission device a in FIG.
In the case of FIG. 5B, the output passing through the modulation / demodulation unit 10 of FIG. 5A becomes as shown in FIG. As can be seen from this figure, this modulation method modulates data "1" by (1/2) f and data "0" by the frequency of f.

Then, as shown in FIG. 5 (D), the data passing through the differential transceiver 9 is output to the transmission line 1 as a positive / negative pulse train with 0V as a reference. In the process of passing through the transmission line 1, the transmission device 1 and the pulse transformer 4 cause a load on the transmission device b.
At the time of receiving data, the transmission waveform is distorted as shown in FIG. Then, in the transmission waveform that has entered the differential transceiver 9, the positive and negative portions are "1" with 0V as a reference,
Convert to "0". That is FIG. 5 (F). The waveform output from the modulator / demodulator becomes the transmitted data of "1" and "0" as shown in FIG. 5 (G). Next, OF
There are also some known methods for distinguishing the CF and CF from the data part.

One is to set a specific bit string as a flag.
In this case, the bit string of the data may match, so if the data part has the same bit string as the flag, 1
Bits are added to prevent the same bit string as the flag. Therefore, a circuit for adding 1 bit at the time of transmission or deleting 1 bit at the time of reception is required in the transmission circuit, and more bit width of the flag is necessary to prevent the bit string of data from matching the flag. Becomes

A method is also known in which OF and CF are set to be lower than the frequency f of data to distinguish them from the data part. In this case, since the flag and the data part do not coincide with each other, the circuit as described above is not necessary, the bit width occupied by OF and CF is reduced, and the extra bit is not added in the data part, so that the transmission efficiency is improved. Get better.

When a pulse as shown in FIG. 6 (A) is sent from the transmitting end under such a method, a waveform as shown in FIG. 6 (B) is observed at the receiving end if the transmission path is sufficiently short. To be done. The lowering of the level from 0 V in FIG. 6 (B) to the negative side affects the waveform distortion. This is shown in FIG. For example, in this case, the transmission line has a long distance, but as shown in FIG. 7 (A), when the transmission line is in the floating state, an OF pulse is transmitted, and then a “0” data is transmitted. As shown in FIG. 7 (B), the waveform at the end causes a waveform distortion in which the initial fall of OF to the negative side affects the subsequent pulse and lowers the overall level. As a result, as shown in FIG. 7 (C), the duty of the pulse is lost and the data cannot be transmitted correctly.

Further, as shown in FIG. 8 (A), when a wide pulse such as CF is sent after sending data, the transmission waveform at the receiving end becomes as shown in FIG. 8 (B), and demodulation is performed. The input becomes as shown in Fig. 8 (C), and since much residual magnetic flux remains in the pulse transformer, it takes time for the transmission line to float, and the transmission efficiency deteriorates, or the residual magnetic flux affects the next frame. Waveform distortion.

[Problems to be solved by the invention]

As described above, in the conventional multi-drop data transmission using the pulse transformer, the frequency of the open flag (OF) indicating the beginning of the frame and the frequency of the close flag (CF) indicating the end of the frame are set as data (“1” / “”). By setting the frequency lower than 0 "), in the data transmission method using the modulation method for identifying the frame, there are problems of waveform distortion at the time of data transmission and a drawback that the transmission path after data transmission is greatly affected. there were.

Therefore, in the present invention, these conventional defects are improved,
By reducing the waveform distortion during data transmission and reducing the influence on the transmission line after data transmission, it is intended to enable highly reliable and high-speed data transmission.

[Means for solving problems]

The present invention is data transmission of a multi-drop method using a pulse transformer, and the frequency of an open flag (OF) indicating the beginning of a frame and a close flag (CF) indicating the end of the frame is set as data (“1” / “0”). In the data transmission method using the modulation method for identifying a frame, an even number of OF signals are transmitted, and an even number of pulse signals having a higher frequency than the CF signal are transmitted after the CF signal. By doing so, a data transmission method that reduces the influence on the transmission path after frame transmission is provided.

[Work]

In the configuration of the above invention, by transmitting an even number of OF signals, the effect (waveform distortion) of the OF signals on data transmission is reduced, and even number of pulse signals having a higher frequency than the CF signal are transmitted after the CF signal. By doing
The influence of the residual magnetic flux stored in the pulse transformer can be reduced and the transmission line can be quickly brought into a balanced state.

〔Example〕

 FIG. 1 shows a waveform diagram of an embodiment of the present invention.

FIG. 1 (A) shows a transmission waveform at the transmitting end of this embodiment, in which two OFs before data are provided. As described in FIG. 7, change the OF from the floating state to 1
In the case of only the number of pulses, the pulse train of the following data is affected, but as in the present embodiment, by setting two OFs, two drops on the negative side caused by the first OF are dropped. It is made smaller by the OF of the eyes. As a result, as shown in FIG. 1 (B), in the transmission waveform at the receiving end, the deviation of the data pulse train to the negative side becomes smaller, and FIG. 1 (C)
As shown in, it is possible to reduce the influence on the duty of the pulse entering the demodulation input.

Although the number of OFs is set to two this time, if the number is even, the number of OFs can be increased to reduce the influence on the transmission path.

FIG. 2 is an example of reducing the influence of CF at the end of transmission in the embodiment according to the present invention. FIG. 2 (A) shows the same frequency as “0” after CF at the transmission end after the end of transmission. 4 pulses are added. As shown in the waveform diagram of FIG. 2 (B), the residual magnetic flux accumulated by the CF is released by applying voltages of different polarities alternately by the following four pulses, and the transmission line is quickly balanced. I have to. As a result, the duty deviation of the pulse of the demodulation input in FIG. 2 (C) is reduced, and the data is transmitted correctly.

Here, the pulse added after CF is an even number of pulses of high frequency, but the more pulses, the faster the equilibrium state is reached.

〔The invention's effect〕

As described above, according to the present invention, by transmitting an even number of OF signals, it is possible to reduce the influence (waveform distortion) of the OF signals on the data signal and to perform highly reliable data transmission. Further, by transmitting an even number of pulse signals having a frequency higher than that of the CF signal after the CF signal, the influence of the residual magnetic flux accumulated in the pulse transformer is reduced, the transmission line is quickly in an equilibrium state, and high-speed data transmission is possible. It will be possible.

[Brief description of drawings]

1 (A) to (C) are waveform diagrams showing an embodiment for reducing the influence of OF in the floating state according to the present invention, and FIGS. 2 (A) to (C) are due to CF at the end of transmission according to the present invention. FIG. 3 is a waveform diagram showing an embodiment for reducing the influence, FIG. 3 is a configuration diagram of a multi-drop system, FIG. 4 is a configuration diagram of a frame in the multi-drop system, and FIG. 5 (A) is a configuration of a transmission device in the multi-drop system. Figure, Figure 5 (B) ~
(G) is an explanatory diagram of modulation / demodulation waveforms of the PDM system, FIGS. 6 (A) to 6 (B) are single pulse transmission waveform diagrams, and FIG. 7 (A).
8A to 8C are diagrams showing the influence of OF in the conventional floating state, and FIGS. 8A to 8C are diagrams showing the influence of CF at the end of transmission. 1 ... Transmission path 2 ... Terminal resistance 3 ... Transmission device 4 ... Pulse transformer 5 ... Frame 6 ... Open flag (OF) 7 ... Data 8 ... Close flag (CF) 9 ... Differential transceiver 10 ... Modulator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Chihiro Nakajima 1 Fuji-cho, Hino-shi, Tokyo Inside Fuji Huacom Control Co., Ltd. (72) Inventor Yasushi Ishii 1-1 Tanabe Nitta, Kawasaki-ku, Kanagawa Prefecture Fuji Electric Within the corporation

Claims (1)

[Claims] 1. In multi-drop data transmission using a pulse transformer, the frequencies of an open flag (OF) indicating the beginning of a frame and a close flag (CF) indicating the end of the frame are set as data ("1" / "0"). In the data transmission method using the modulation method for identifying a frame, the number of OF signals is even, and after the CF signal, an even number of pulse signals having a higher frequency than the CF signal are transmitted. A data transmission method characterized by transmitting.